Washington, November 14 Two teams of astronomers have found that extrasolar planet HAT-P-7b, discovered in 2008, has a retrograde or highly tilted orbit.

On May 30, 2009, a Japanese collaboration team led by Norio Narita (National Astronomical Observatory of Japan) used the Subaru Telescope's High Dispersion Spectrograph (HDS) to observe the HAT-P-7 planetary system, which is about 1000 light-years distant from Earth, and found the first evidence of a retrograde orbit of the extrasolar planet HAT-P-7b.

On July 1, 2009, a US collaboration team led by Joshua N. Winn (Massachusetts Institute of Technology) also used the Subaru Telescope's HDS to independently observe the HAT-P-7 system and likewise concluded that extrasolar planet HAT-P-7b has a retrograde or polar orbit.

Both observational results were independently submitted and accepted to scientific journals in August 2009, and were published in October 2009.

The HAT-P-7b is the first planet that indicates a retrograde orbit at the time of publications in scientific journals.

Such retrograde or spin-orbit misaligned planets are important for understanding the diversity of planetary systems, and they provide important evidence for assessing current planetary migration models.

It is now well known that extrasolar planets have diverse orbits, and recent planetary migration models have predicted the existence of such a retrograde extrasolar planet.

The Subaru findings provide an important milestone for understanding the orbital evolution of planetary systems. (ANI)